Electrical discharge device



Q. W. LIVINGSTON ELECTRICAL DISCHARGE DEVICE Filed Oct. 22, 1936 CONTROL POTENTIAL In ventor:

I5 Attorney.

potential encountered in actual practice.

Patented Mar. 22, 1938 EEEUWCAL DISCHARGE DEVHCE @rrin W. Livingston, Schenectady, N. Y, assignor to General Electric Company, a corpora tion of New York Application @ctober 2a was, Serial No. roasts 9 Diaims.

The present invention relates, to electrical discharge devices, and more particularly to discharge devices which include an ionizable gas or vapor as an operating medium. Devices within this latter classification are normally characterized by the fact that while a. discharge may be initiated by the action of the control electrode alone, it. may be interrupted only by reducing the anode potential below a critical value.

10 In connection with many uses of discontinuously controlled discharge devices of the type specified, it has been observed that their control characteristics tend to be objectionably affected by the sporadic variations in anode to cathode In certain cases extreme changes in anode potential occasioned by circuit transients may cause a discharge to be initiated independently of the control electrode potential while, in other cases, po-

tentlal variations which are insufiicient to overcome the effect of the control electrode may so modify the critical control voltage at which a discharge can take place'as to render the operation of the device unreliable.

In Patents No. 2,044,618 and 2,Q44,619, assigned to the General Electric Company, I have disclosed and claimed means for shielding the control electrode in such a manner that the first of the abovedescribed efiects may be substantially overcome.

The present invention is more specifically concerned with the second efiect and has for an object the prevention of variations of the critical discharge-initiating voltage of the control electrode with changing anode potential.

5 It is a further object of the invention to shield the control electrode from the main discharge electrodes in such a way that the initiation of a discharge will depend only upon the charging of the control electrode to a constant predetermined 4o voltage.

'Itis a still further object to provide in the vicinity of the control electrode an electrostatic field adapted toiavor the initiation of a discharge upon the attainment of a given critical control 45 electrode potential, irrespective of variations in the potential of the anode.

The features of novelty which I desire to protect herein'are pointed out with particularity in the appended claims. The invention'itself, however,

50 together with further objects and advantages thereof, may best be understood by reference to the tollowing specification taken in connection with the drawing in which Fig. 1 represents in section a discharge device and associated circuit 55 suitably embodying the invention, Fig, 2 illustrates similarly a modified construction of the discharge device and an alternative arrangement of the associated circuit, and Fig. 3 is a graph illustrating certain characteristics of the device shown in Figs. 1 and 2. i d

Referring particularly to Fig. 1, I have shown a sealed envelope l suitably of glass terminating at its lower end in a. reentrant stem 2 and a press 3. Withinthe envelope there are provided main discharge electrodes including an anode t and a 1g cathode of which the latter may suitably comprise an outer cylindrical member enclosing ex,- tended electron emissive surfaces heated indirectly by a means which is indicated diagrammatically as a filamentary resistance wire 8 disis posed axially within the cylinder. An example of such a cathode is described and claimed in A. W. Hull Patent 1,924,319. The anode is provided with a suitable lead-in connection it and similar connections it, it, and i5 are sealed through the pressv 3 and connected to the various elements of the cathode. Between the anode and cathode and surrounding the discharge path which is defined between them there is arranged an electrostatic control member or electrode ll comprising in the particular case illustrated an annular graphite member supported on a lead-in connection 18. In order. to provide a suitable operating medium for these various electrodes, the envelope as a whole may contain a substantial quantity of 30 a gas, for example,-argon, or a small quantity of a readily vaporizableionizing medium, for example, mercury. If this last-named substance is employed, it may be introduced as a small globule (indicated at the base of the envelope by the numeral 20).

In order to shield the control electrode W from the electrostatic field of the anode 6 and thereby to prevent variations in the control characteristic of the tube, my invention provides electrically independent shielding means respectively interposed between the control electrode and the anode and between the control electrode and the oathode. In the particular case illustrated these, means comprise a pair of longitudinally extend- .45 ing metal tubular members 23 and 24 which define a shielding chamber susbtantially enclosing the control electrode. Taken conjointly, these tubular members laterally enclose not only the control electrode but also the entire discharge path up to and including both the anode and cathode so that the complete absence of stray fields proceeding from either of the main discharge electrodes is assured.

T e tubular members 23 and 24 are respectively 5 provided with transverse metal baflies 25 and 21, which have small central apertures and which may be secured in place in any suitable and wellknown manner. To maintain each of the composite shielding means in proper position with respect to the remaining electrodes conductive supports 28 and 29, 30 and 3| are provided, which supports in turn are mounted on the stem tube 2 by means of clips or rings 33 and 34. One member of each pair of supports is connected to a suitable lead-in connection whereby desired potentials may be impressed on the shielding members 23 and 24.

One mode of utilizing the discharge device described in the foregoing is indicated by the circuit connections diagrammatically shown in Fig. 1. According to the arrangement illustrated, the cathode is supplied with exciting current by means of a heating transformer having a primary 35 and a secondary 36. A suitable value of alternating potential derived from the secondary of another transformer 31 is impressed between the cathode and the anode 6 in series with a translating device such, for example, as a solenoidcontrolled circuit breaker or relay. The impedance characteristics of such a device are indicated schematically by a resistance 38 and the parallel combination'of a resistance 39 and an inductance 40. As a result of the inductive component of the impedance, transient voltage variations are apt to appear between the anode 6 and the cathode from cycle to cycle after a discharge is once initiated. For this reason the potential required to be impressed on the control electrode I! to maintain the device recurrently conductive after a discharge has been started may be considerably difierent from that required to initiate the discharge. i

The significance of this fact may best be understood with reference to a particular control circuit such, for example, as that shown in. the drawing. In this circuit there is included a photo-sensitive member 48 arranged as one of the arms of a bridge arrangement which also comprises a. voltage source 49 and balancing resistances 50 and 5|. When the photo-sensitive element is subjected to a light impulse of given intensity its resistance will change, the'bridge be thrown out of balance, and a discharge initiating potential impressed on the control electrode I! through the grid current limiting resistor 52. The setting of the bridge may be such that a definitely predetermined light intensity will be required to cause the initiation of a discharge. However, if the load connected in circuit with the discharge device comprises a relay having the impedance characteristics previously indicated, a decrease in light intensity considerably below the discharge-initiating value may be required before the relay will be again deenergized.

In accordance with my present, invention this lag eflect, which is obviously objectionable, may be avoided by arranging electrostatic members such as members 23 and 24 on opposite sidesof the control electrode and biasing these members positively with respect to the cathode as indicated in Fig. 1. According to the arrangement there shown the member 24 and its associated baiiie portion 2'! are maintained at a slight positive potential with respect to the cathode l by means 01 a source of direct current biasing voltage 54, while the member 23 is maintained at a *stiil higher positive potential by means 01' an additional voltage source 53 which is in series with the source 54. In this way the control electrode i1 is electrostatically shielded from the eile'cts of the field in the region of the anode 5, and at the same time a constant accelerating field independent of anode potential is maintained in the chamber surrounding the aforesaid electrode. Thus, electrons drawn from the cathode l by the eflect of the positive charge maintained on the member 24 may pass through the apertured bail'le 21 into the control electrode chamber where they will be subjected to a definite accelerating potential whose value depends upon the relative'voltages of the members 23 and 24. While this accelerating potential will not ordinarily be sufficient to produce ionization of the operating medium, its presence will insure the result that when a predetermined critical voltage is applied to the control element l1 enough additional velocity will be imparted to the slowly drifting electrons to cause ionization to occur and a main discharge to be initiated. This critical voltage will be independent of the potential existing on the anode 6 (provided of course that that potential is positive and above the ionization potential of the particular operating medium employed) and will be constant for all normal conditions of operation of the discharge device.

An alternative modification of the invention is shown in Fig. 2 in which elements corresponding to those shown in Fig. 1 are similarly numbered. In this embodiment the side walls of the enclosing envelope comprise a pair of tubular metal members 55 and 55 which are insulatingly spaced by a ring of glass 51 sealed to their adjacent extremities. In this case a control electrode 59 is supported between the anode 5 and the cathode 1 by means of lead-in 1 connection 6| sealed through the wall-of the glass ring. The ends of the envelope are hermetically closed by means of flanged headers 62 and 63 respectively joined to the extremities of the tubular members 55 and 55. Each of these headers is provided with means for making lead-in connections to the main discharge electrodes, and the lower header bears a depending tubulation 55 which serves during the manufacturing process to exhaust and finally seal the envelope. It will be seen that the tubular members 55 and 55 also constitute a portion of the walls of a chamber which is so formed as to surround the control electrode 59 and which corresponds to the similar chamber described in connection with Fig. 1. .As in the previously described arrangement, bames 54 and 55 are provided interposed respectively between the control electrode and the anode and between the control electrode and the cathode.

The energizing circuit shown diagrammatically in connection with Fig. 2 is adapted to avoid the necessity of a supply of direct current biasing potential. To this end a portion of the potential of a transformer I0 is impressed across a potentiometer resistance II which is connected in series with an additional current limiting resistance 12. Portions of the voltage developed across the resistor H are impressed on the tubular members 55 and 55 by means of connections 14 and 15. The order 01" connection is such that these members are positively charged with respect to the cathode whenever the anode is similarly charged. If desired the values of the various sections of the resistor Il may be so adjusted that only a slight accelerating voltage is developed across the shielding members or alternatively this voltage may be given a higher value such that the potential of the member 55 and its associated baille 65 exceeds the ionization voltage of the operating medium in the envelope. If the latter condition is chosen, the device may be maintained nonconductive by the use of a negative bias impressed on the control electrode 59, and a control or triggering apparatus 16, corresponding for example to the control circuit shown in Fig. 1, may be utilized which is of such nature as to release this negative bias upon proper stimulation thereby to permit a discharge to take place. Under the conditions assumed such a discharge will first occur between the cathode i and the positive shielding member 55 (or the baflie 65) from which it may be caused to transfer to the main anode 6 by the use of a suificiently high resistance 18 interposed in the lead 14.

In order to limit the biasing voltage applied to the shielding members to a predetermined constant value means represented as a glow discharge device 8| may be connected across the resistor H for governing the potential impressed thereon. The characteristics of a glow discharge device are such that it will become conductive at a definite predeterminable voltage and thereafter will support across its terminals a substantially constant voltage slightly lower in value than the breakdown voltage. Consequently the potential developed across resistance ill will not be permitted to rire to a value in excess of the drop across the device 3| irrespective of the variations in voltage current between the anode 6 and the cathode 1. As

.an ultimate result of these provisions the field in the vicinity of the control electrode 59 may be maintained substantially constant during the periods in which the discharge device as a whole is capable of being rendered conductive, and the initiation of a discharge will depend in all cases upon the application to such control electrode of a perfectly definite and predeterminable starting voltage. a

The advantageous results of my invention may best be understood by reference to Fig. 3 in which I have shown curves A and B representing respectively variations of critical grid'voltage with anode voltage for an unshielded control member and for a control member shielded in the manner described in the foregoing. It will be seen that whereas in curve A a considerable change in the control potential required to initiate a discharge occurs for a given variation in anode potential, in curve B a control characteristic is obtained which is substantially independent of anode potential.

While I have shown particular embodiments of my invention, it will be understood by those skilled in the art that many modifications may be made without departing from the invention,

and I aim by the appended claims to cover all,

such modifications as fall within the true spirit and scope of the invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. In an electrical discharge device, an envelope containing a substantial quantity of an ionizable medium, an anode and a cathode arranged within said envelope and defining a discharge path, an electrostatic control member associated with said discharge path and a chamber substantially enclosing said control member, said cham ber comprising a pair of electrically independent conducting members each laterally surrounding said discharge path and a pair of transverse conducting baiiles each secured to one of said conducting members and adapted during the operation of said device to shield the control element from the eifects of variations in potential of said anode.

2. In an electrical discharge device including relatively spaced anode and cathode members defining a discharge path therebetween, an electrostatic control member between said anode and cathode and electrostatic shielding means associated with said control member, said means comprising a pair of electrically independent metal tubular members conjointly laterally enclosing said anode and cathode and said discharge path, and a pair of transverse apertured 'metal bailles each secured to one of said tubular members and respectively interposed between said contro member and said anode and cathode.

3. An electrical discharge device comprising a sealed envelope, an anode and a cathode arranged within said envelope, an electrostatic control member between said anode and cathode and a chamber substantially enclosing said control member, said chamber comprising a pair of elec trically independent conducting members which also constitute portions of the wall of said envelope and a pair of transverse electrostatic shielding members each connected to one of said conducting members and respectively interposed between the control member and said anode and the control member and said cathode.

4. An electrical discharge device comprising an elongated envelope enclosing spaced anode and cathode electrodes, a pair of tubular metal members forming portions of the wall of said envelope, means electrically insulating said tubular members from one another, an electrostatic control electrode interposed between the anode and cathode, and a chamber substantially enclosing said control electrode, said chamber being formed partly by portions of said tubular members and partly by a pair of apertured transverse metal baiiies each electrically connected to one of the tubular members and interposed between the control electrode and said anode and cathode respectively.

5. In an electrical discharge device, an envelope containing a substantial quantity of an ionizable medium, an anode and a cathode arranged within said envelope and adapted to support a discharge therebetween, a control electrode between said anode and cathode and adapted to control the initiation of a discharge during certain periods of the operation of said device, and means effective at least during said certain periods to maintain in the vicinity of said control electrode a substantially constant accelerating field the magnitude of which is independent of variations in the potential of said anode.

6. In an electrical discharge device, an envelope containing a substantial quantity of an ionizable medium, an anode and a cathode arranged within said envelope to support a discharge therebetween, a control electrode between said anode and cathode and adapted to control the initiation of a discharge during certain periods of the operation of said device, and means including electrostatic members arranged on opposite sides of said control electrode effective at least during said velope and adapted to support a discharge therebetween, a control electrode between said anode and cathode and adapted to control the initiation of a discharge during-certain periods 01' the operation of said device, a shielding member interposed between the control electrode and said cathode, a second shielding member electrically independent of the first and interposed between the control electrode and said anode, and means eflective at least during said certain periods to maintain said shielding members at predetermined positive potentials with respect to the cathode, the potential of said second member being higher than that of the first.

8. In combination, an electrical discharge device comprising an envelope containing a substantial quantity of an ionizable medium, an anode and a cathode arranged within said envelope and adapted to support a discharge therebetween, a control electrode between said anode and cathode and adapted to control the initiation of a discharge therebetween, a shielding member interposed between the control electrode and said cathode, a second shielding member electrically independent of the first and interposed between the control electrode and said anode, means including a source of alternating potential for producing intermittent discharges between said anode and cathode during the recurrent intervals when the anode is positive with respect to the cathode, means for impressing a discharge-initiating potential on said control electrode in desired relation to the variations of said alternating potential, and means including a source of biasing potential for maintaining said shielding members at predetermined positive potentials with respect to said cathode during said recurrent intervals, the potential of said second member being higher than that of the first.

9. In combination, an electrical discharge device comprising an envelope containing an ionizable medium, an anode, and a cathode arranged within said envelope and adapted to support a discharge therebetween, a control electrode between said anode and cathode and adapted to control the initiation of a discharge, a shielding member interposed between the control electrode and said cathode, a second shielding member electrically independent oi the first and interposed between the control electrode and said anode, means including a source of alternating potential for producing intermittent discharges between said anode and cathode during the recurrent intervals when the anode is positive with respect to the cathode, means for impressing a discharge-controlling potential on said control electrode in desired relation to the variations of said alternating potential, means including said source of alternating current for impressing biasing potentials on said shielding members during said recurrent intervals, and means for limiting said biasing potentials to a desiredvalue.

ORRIN W. LIVINGSTON. 

